rust-lang · ChayimFriedman2 · Aug 14, 2025
diff --git a/compiler/rustc_middle/src/ty/context.rs b/compiler/rustc_middle/src/ty/context.rs
@@ -52,7 +52,7 @@ use rustc_session::{Limit, Session};
 use rustc_span::def_id::{CRATE_DEF_ID, DefPathHash, StableCrateId};
 use rustc_span::{DUMMY_SP, Ident, Span, Symbol, kw, sym};
 use rustc_type_ir::TyKind::*;
-use rustc_type_ir::lang_items::TraitSolverLangItem;
+use rustc_type_ir::lang_items::{TraitSolverLangItem, TraitSolverTraitLangItem};
 pub use rustc_type_ir::lift::Lift;
 use rustc_type_ir::{
     CollectAndApply, Interner, TypeFlags, TypeFoldable, WithCachedTypeInfo, elaborate, search_graph,
@@ -93,6 +93,7 @@ impl<'tcx> Interner for TyCtxt<'tcx> {
 
     type DefId = DefId;
     type LocalDefId = LocalDefId;
+    type TraitId = DefId;
     type Span = Span;
 
     type GenericArgs = ty::GenericArgsRef<'tcx>;
@@ -481,19 +482,31 @@ impl<'tcx> Interner for TyCtxt<'tcx> {
     }
 
     fn require_lang_item(self, lang_item: TraitSolverLangItem) -> DefId {
-        self.require_lang_item(trait_lang_item_to_lang_item(lang_item), DUMMY_SP)
+        self.require_lang_item(trait_lang_item_to_solver_lang_item(lang_item), DUMMY_SP)
+    }
+
+    fn require_trait_lang_item(self, lang_item: TraitSolverTraitLangItem) -> DefId {
+        self.require_lang_item(trait_lang_item_to_solver_trait_lang_item(lang_item), DUMMY_SP)
     }
 
     fn is_lang_item(self, def_id: DefId, lang_item: TraitSolverLangItem) -> bool {
-        self.is_lang_item(def_id, trait_lang_item_to_lang_item(lang_item))
+        self.is_lang_item(def_id, trait_lang_item_to_solver_lang_item(lang_item))
+    }
+
+    fn is_trait_lang_item(self, def_id: DefId, lang_item: TraitSolverTraitLangItem) -> bool {
+        self.is_lang_item(def_id, trait_lang_item_to_solver_trait_lang_item(lang_item))
     }
 
     fn is_default_trait(self, def_id: DefId) -> bool {
         self.is_default_trait(def_id)
     }
 
     fn as_lang_item(self, def_id: DefId) -> Option<TraitSolverLangItem> {
-        lang_item_to_trait_lang_item(self.lang_items().from_def_id(def_id)?)
+        solver_lang_item_to_trait_lang_item(self.lang_items().from_def_id(def_id)?)
+    }
+
+    fn as_trait_lang_item(self, def_id: DefId) -> Option<TraitSolverTraitLangItem> {
+        solver_trait_lang_item_to_trait_lang_item(self.lang_items().from_def_id(def_id)?)
     }
 
     fn associated_type_def_ids(self, def_id: DefId) -> impl IntoIterator<Item = DefId> {
@@ -724,57 +737,70 @@ impl<'tcx> Interner for TyCtxt<'tcx> {
 }
 
 macro_rules! bidirectional_lang_item_map {
-    ($($name:ident),+ $(,)?) => {
-        fn trait_lang_item_to_lang_item(lang_item: TraitSolverLangItem) -> LangItem {
+    (
+        $solver_ty:ident, $to_solver:ident, $from_solver:ident;
+        $($name:ident),+ $(,)?
+    ) => {
+        fn $from_solver(lang_item: $solver_ty) -> LangItem {
             match lang_item {
-                $(TraitSolverLangItem::$name => LangItem::$name,)+
+                $($solver_ty::$name => LangItem::$name,)+
             }
         }
 
-        fn lang_item_to_trait_lang_item(lang_item: LangItem) -> Option<TraitSolverLangItem> {
+        fn $to_solver(lang_item: LangItem) -> Option<$solver_ty> {
             Some(match lang_item {
-                $(LangItem::$name => TraitSolverLangItem::$name,)+
+                $(LangItem::$name => $solver_ty::$name,)+
                 _ => return None,
             })
         }
     }
 }
 
 bidirectional_lang_item_map! {
+    TraitSolverLangItem, solver_lang_item_to_trait_lang_item, trait_lang_item_to_solver_lang_item;
+
+// tidy-alphabetical-start
+    AsyncFnKindUpvars,
+    AsyncFnOnceOutput,
+    CallOnceFuture,
+    CallRefFuture,
+    CoroutineReturn,
+    CoroutineYield,
+    DynMetadata,
+    FutureOutput,
+    Metadata,
+    Option,
+    Poll,
+// tidy-alphabetical-end
+}
+
+bidirectional_lang_item_map! {
+    TraitSolverTraitLangItem, solver_trait_lang_item_to_trait_lang_item, trait_lang_item_to_solver_trait_lang_item;
+
 // tidy-alphabetical-start
     AsyncFn,
     AsyncFnKindHelper,
-    AsyncFnKindUpvars,
     AsyncFnMut,
     AsyncFnOnce,
     AsyncFnOnceOutput,
     AsyncIterator,
     BikeshedGuaranteedNoDrop,
-    CallOnceFuture,
-    CallRefFuture,
     Clone,
     Copy,
     Coroutine,
-    CoroutineReturn,
-    CoroutineYield,
     Destruct,
     DiscriminantKind,
     Drop,
-    DynMetadata,
     Fn,
     FnMut,
     FnOnce,
     FnPtrTrait,
     FusedIterator,
     Future,
-    FutureOutput,
     Iterator,
     MetaSized,
-    Metadata,
-    Option,
     PointeeSized,
     PointeeTrait,
-    Poll,
     Sized,
     TransmuteTrait,
     Tuple,

diff --git a/compiler/rustc_next_trait_solver/src/coherence.rs b/compiler/rustc_next_trait_solver/src/coherence.rs
@@ -295,7 +295,7 @@ where
         ControlFlow::Break(OrphanCheckEarlyExit::UncoveredTyParam(ty))
     }
 
-    fn def_id_is_local(&mut self, def_id: I::DefId) -> bool {
+    fn def_id_is_local(&mut self, def_id: impl DefId<I>) -> bool {
         match self.in_crate {
             InCrate::Local { .. } => def_id.is_local(),
             InCrate::Remote => false,

diff --git a/compiler/rustc_next_trait_solver/src/solve/assembly/mod.rs b/compiler/rustc_next_trait_solver/src/solve/assembly/mod.rs
@@ -7,7 +7,7 @@ use std::ops::ControlFlow;
 
 use derive_where::derive_where;
 use rustc_type_ir::inherent::*;
-use rustc_type_ir::lang_items::TraitSolverLangItem;
+use rustc_type_ir::lang_items::TraitSolverTraitLangItem;
 use rustc_type_ir::solve::SizedTraitKind;
 use rustc_type_ir::{
     self as ty, Interner, TypeFlags, TypeFoldable, TypeSuperVisitable, TypeVisitable,
@@ -52,7 +52,7 @@ where
 
     fn with_replaced_self_ty(self, cx: I, self_ty: I::Ty) -> Self;
 
-    fn trait_def_id(self, cx: I) -> I::DefId;
+    fn trait_def_id(self, cx: I) -> I::TraitId;
 
     /// Consider a clause, which consists of a "assumption" and some "requirements",
     /// to satisfy a goal. If the requirements hold, then attempt to satisfy our
@@ -490,80 +490,82 @@ where
         } else if cx.trait_is_alias(trait_def_id) {
             G::consider_trait_alias_candidate(self, goal)
         } else {
-            match cx.as_lang_item(trait_def_id) {
-                Some(TraitSolverLangItem::Sized) => {
+            match cx.as_trait_lang_item(trait_def_id) {
+                Some(TraitSolverTraitLangItem::Sized) => {
                     G::consider_builtin_sizedness_candidates(self, goal, SizedTraitKind::Sized)
                 }
-                Some(TraitSolverLangItem::MetaSized) => {
+                Some(TraitSolverTraitLangItem::MetaSized) => {
                     G::consider_builtin_sizedness_candidates(self, goal, SizedTraitKind::MetaSized)
                 }
-                Some(TraitSolverLangItem::PointeeSized) => {
+                Some(TraitSolverTraitLangItem::PointeeSized) => {
                     unreachable!("`PointeeSized` is removed during lowering");
                 }
-                Some(TraitSolverLangItem::Copy | TraitSolverLangItem::Clone) => {
+                Some(TraitSolverTraitLangItem::Copy | TraitSolverTraitLangItem::Clone) => {
                     G::consider_builtin_copy_clone_candidate(self, goal)
                 }
-                Some(TraitSolverLangItem::Fn) => {
+                Some(TraitSolverTraitLangItem::Fn) => {
                     G::consider_builtin_fn_trait_candidates(self, goal, ty::ClosureKind::Fn)
                 }
-                Some(TraitSolverLangItem::FnMut) => {
+                Some(TraitSolverTraitLangItem::FnMut) => {
                     G::consider_builtin_fn_trait_candidates(self, goal, ty::ClosureKind::FnMut)
                 }
-                Some(TraitSolverLangItem::FnOnce) => {
+                Some(TraitSolverTraitLangItem::FnOnce) => {
                     G::consider_builtin_fn_trait_candidates(self, goal, ty::ClosureKind::FnOnce)
                 }
-                Some(TraitSolverLangItem::AsyncFn) => {
+                Some(TraitSolverTraitLangItem::AsyncFn) => {
                     G::consider_builtin_async_fn_trait_candidates(self, goal, ty::ClosureKind::Fn)
                 }
-                Some(TraitSolverLangItem::AsyncFnMut) => {
+                Some(TraitSolverTraitLangItem::AsyncFnMut) => {
                     G::consider_builtin_async_fn_trait_candidates(
                         self,
                         goal,
                         ty::ClosureKind::FnMut,
                     )
                 }
-                Some(TraitSolverLangItem::AsyncFnOnce) => {
+                Some(TraitSolverTraitLangItem::AsyncFnOnce) => {
                     G::consider_builtin_async_fn_trait_candidates(
                         self,
                         goal,
                         ty::ClosureKind::FnOnce,
                     )
                 }
-                Some(TraitSolverLangItem::FnPtrTrait) => {
+                Some(TraitSolverTraitLangItem::FnPtrTrait) => {
                     G::consider_builtin_fn_ptr_trait_candidate(self, goal)
                 }
-                Some(TraitSolverLangItem::AsyncFnKindHelper) => {
+                Some(TraitSolverTraitLangItem::AsyncFnKindHelper) => {
                     G::consider_builtin_async_fn_kind_helper_candidate(self, goal)
                 }
-                Some(TraitSolverLangItem::Tuple) => G::consider_builtin_tuple_candidate(self, goal),
-                Some(TraitSolverLangItem::PointeeTrait) => {
+                Some(TraitSolverTraitLangItem::Tuple) => {
+                    G::consider_builtin_tuple_candidate(self, goal)
+                }
+                Some(TraitSolverTraitLangItem::PointeeTrait) => {
                     G::consider_builtin_pointee_candidate(self, goal)
                 }
-                Some(TraitSolverLangItem::Future) => {
+                Some(TraitSolverTraitLangItem::Future) => {
                     G::consider_builtin_future_candidate(self, goal)
                 }
-                Some(TraitSolverLangItem::Iterator) => {
+                Some(TraitSolverTraitLangItem::Iterator) => {
                     G::consider_builtin_iterator_candidate(self, goal)
                 }
-                Some(TraitSolverLangItem::FusedIterator) => {
+                Some(TraitSolverTraitLangItem::FusedIterator) => {
                     G::consider_builtin_fused_iterator_candidate(self, goal)
                 }
-                Some(TraitSolverLangItem::AsyncIterator) => {
+                Some(TraitSolverTraitLangItem::AsyncIterator) => {
                     G::consider_builtin_async_iterator_candidate(self, goal)
                 }
-                Some(TraitSolverLangItem::Coroutine) => {
+                Some(TraitSolverTraitLangItem::Coroutine) => {
                     G::consider_builtin_coroutine_candidate(self, goal)
                 }
-                Some(TraitSolverLangItem::DiscriminantKind) => {
+                Some(TraitSolverTraitLangItem::DiscriminantKind) => {
                     G::consider_builtin_discriminant_kind_candidate(self, goal)
                 }
-                Some(TraitSolverLangItem::Destruct) => {
+                Some(TraitSolverTraitLangItem::Destruct) => {
                     G::consider_builtin_destruct_candidate(self, goal)
                 }
-                Some(TraitSolverLangItem::TransmuteTrait) => {
+                Some(TraitSolverTraitLangItem::TransmuteTrait) => {
                     G::consider_builtin_transmute_candidate(self, goal)
                 }
-                Some(TraitSolverLangItem::BikeshedGuaranteedNoDrop) => {
+                Some(TraitSolverTraitLangItem::BikeshedGuaranteedNoDrop) => {
                     G::consider_builtin_bikeshed_guaranteed_no_drop_candidate(self, goal)
                 }
                 _ => Err(NoSolution),
@@ -574,7 +576,7 @@ where
 
         // There may be multiple unsize candidates for a trait with several supertraits:
         // `trait Foo: Bar<A> + Bar<B>` and `dyn Foo: Unsize<dyn Bar<_>>`
-        if cx.is_lang_item(trait_def_id, TraitSolverLangItem::Unsize) {
+        if cx.is_trait_lang_item(trait_def_id, TraitSolverTraitLangItem::Unsize) {
             candidates.extend(G::consider_structural_builtin_unsize_candidates(self, goal));
         }
     }

diff --git a/compiler/rustc_next_trait_solver/src/solve/assembly/structural_traits.rs b/compiler/rustc_next_trait_solver/src/solve/assembly/structural_traits.rs
@@ -4,7 +4,7 @@
 use derive_where::derive_where;
 use rustc_type_ir::data_structures::HashMap;
 use rustc_type_ir::inherent::*;
-use rustc_type_ir::lang_items::TraitSolverLangItem;
+use rustc_type_ir::lang_items::{TraitSolverLangItem, TraitSolverTraitLangItem};
 use rustc_type_ir::solve::SizedTraitKind;
 use rustc_type_ir::solve::inspect::ProbeKind;
 use rustc_type_ir::{
@@ -466,7 +466,7 @@ pub(in crate::solve) fn extract_tupled_inputs_and_output_from_async_callable<I:
                 nested.push(
                     ty::TraitRef::new(
                         cx,
-                        cx.require_lang_item(TraitSolverLangItem::AsyncFnKindHelper),
+                        cx.require_trait_lang_item(TraitSolverTraitLangItem::AsyncFnKindHelper),
                         [kind_ty, Ty::from_closure_kind(cx, goal_kind)],
                     )
                     .upcast(cx),
@@ -508,7 +508,7 @@ pub(in crate::solve) fn extract_tupled_inputs_and_output_from_async_callable<I:
             let args = args.as_closure();
             let bound_sig = args.sig();
             let sig = bound_sig.skip_binder();
-            let future_trait_def_id = cx.require_lang_item(TraitSolverLangItem::Future);
+            let future_trait_def_id = cx.require_trait_lang_item(TraitSolverTraitLangItem::Future);
             // `Closure`s only implement `AsyncFn*` when their return type
             // implements `Future`.
             let mut nested = vec![
@@ -526,7 +526,7 @@ pub(in crate::solve) fn extract_tupled_inputs_and_output_from_async_callable<I:
                 }
             } else {
                 let async_fn_kind_trait_def_id =
-                    cx.require_lang_item(TraitSolverLangItem::AsyncFnKindHelper);
+                    cx.require_trait_lang_item(TraitSolverTraitLangItem::AsyncFnKindHelper);
                 // When we don't know the closure kind (and therefore also the closure's upvars,
                 // which are computed at the same time), we must delay the computation of the
                 // generator's upvars. We do this using the `AsyncFnKindHelper`, which as a trait
@@ -593,7 +593,7 @@ fn fn_item_to_async_callable<I: Interner>(
     bound_sig: ty::Binder<I, ty::FnSig<I>>,
 ) -> Result<(ty::Binder<I, AsyncCallableRelevantTypes<I>>, Vec<I::Predicate>), NoSolution> {
     let sig = bound_sig.skip_binder();
-    let future_trait_def_id = cx.require_lang_item(TraitSolverLangItem::Future);
+    let future_trait_def_id = cx.require_trait_lang_item(TraitSolverTraitLangItem::Future);
     // `FnDef` and `FnPtr` only implement `AsyncFn*` when their
     // return type implements `Future`.
     let nested = vec![
@@ -744,7 +744,7 @@ pub(in crate::solve) fn const_conditions_for_destruct<I: Interner>(
     cx: I,
     self_ty: I::Ty,
 ) -> Result<Vec<ty::TraitRef<I>>, NoSolution> {
-    let destruct_def_id = cx.require_lang_item(TraitSolverLangItem::Destruct);
+    let destruct_def_id = cx.require_trait_lang_item(TraitSolverTraitLangItem::Destruct);
 
     match self_ty.kind() {
         // `ManuallyDrop` is trivially `[const] Destruct` as we do not run any drop glue on it.
@@ -763,7 +763,7 @@ pub(in crate::solve) fn const_conditions_for_destruct<I: Interner>(
                 Some(AdtDestructorKind::NotConst) => return Err(NoSolution),
                 // `Drop` impl exists, and it's const. Require `Ty: [const] Drop` to hold.
                 Some(AdtDestructorKind::Const) => {
-                    let drop_def_id = cx.require_lang_item(TraitSolverLangItem::Drop);
+                    let drop_def_id = cx.require_trait_lang_item(TraitSolverTraitLangItem::Drop);
                     let drop_trait_ref = ty::TraitRef::new(cx, drop_def_id, [self_ty]);
                     const_conditions.push(drop_trait_ref);
                 }
@@ -881,7 +881,7 @@ where
 
     // FIXME(associated_const_equality): Also add associated consts to
     // the requirements here.
-    for associated_type_def_id in cx.associated_type_def_ids(trait_ref.def_id) {
+    for associated_type_def_id in cx.associated_type_def_ids(trait_ref.def_id.into()) {
         // associated types that require `Self: Sized` do not show up in the built-in
         // implementation of `Trait for dyn Trait`, and can be dropped here.
         if cx.generics_require_sized_self(associated_type_def_id) {

diff --git a/compiler/rustc_next_trait_solver/src/solve/effect_goals.rs b/compiler/rustc_next_trait_solver/src/solve/effect_goals.rs
@@ -3,7 +3,7 @@
 
 use rustc_type_ir::fast_reject::DeepRejectCtxt;
 use rustc_type_ir::inherent::*;
-use rustc_type_ir::lang_items::TraitSolverLangItem;
+use rustc_type_ir::lang_items::TraitSolverTraitLangItem;
 use rustc_type_ir::solve::SizedTraitKind;
 use rustc_type_ir::solve::inspect::ProbeKind;
 use rustc_type_ir::{self as ty, Interner, elaborate};
@@ -33,7 +33,7 @@ where
         self.with_replaced_self_ty(cx, self_ty)
     }
 
-    fn trait_def_id(self, _: I) -> I::DefId {
+    fn trait_def_id(self, _: I) -> I::TraitId {
         self.def_id()
     }
 
@@ -233,7 +233,11 @@ where
         // A built-in `Fn` impl only holds if the output is sized.
         // (FIXME: technically we only need to check this if the type is a fn ptr...)
         let output_is_sized_pred = inputs_and_output.map_bound(|(_, output)| {
-            ty::TraitRef::new(cx, cx.require_lang_item(TraitSolverLangItem::Sized), [output])
+            ty::TraitRef::new(
+                cx,
+                cx.require_trait_lang_item(TraitSolverTraitLangItem::Sized),
+                [output],
+            )
         });
         let requirements = cx
             .const_conditions(def_id)

diff --git a/compiler/rustc_next_trait_solver/src/solve/mod.rs b/compiler/rustc_next_trait_solver/src/solve/mod.rs
@@ -130,7 +130,7 @@ where
         }
     }
 
-    fn compute_dyn_compatible_goal(&mut self, trait_def_id: I::DefId) -> QueryResult<I> {
+    fn compute_dyn_compatible_goal(&mut self, trait_def_id: I::TraitId) -> QueryResult<I> {
         if self.cx().trait_is_dyn_compatible(trait_def_id) {
             self.evaluate_added_goals_and_make_canonical_response(Certainty::Yes)
         } else {